Various microelectromechanical systems (MEMS) resonators exist. Conventional methods of coupling complementary metal-oxide-semiconductor (CMOS) circuitry to a MEMS resonator are limited, however, for a variety of reasons. Some MEMS resonators are formed on a first substrate that is later bonded or otherwise electrically coupled to a second CMOS substrate, which subjects the device to alignment issues, MEMS-to-CMOS gap limitations, and additional fabrication costs.
Some other MEMS resonators are integrated directly with CMOS on the same wafer in a side-by-side configuration, meaning the MEMS resonator is typically coplanar with the CMOS or otherwise laterally displaced from the CMOS. Such side-by-side configurations, however, typically require additional die area on the wafer, thereby increasing fabrication costs and design constraints. In addition, conventional MEMS-CMOS monolithic processes typically involve basic, stripped-down CMOS flows that further limit design possibilities and the possible materials that may be effectively used for the MEMS resonator.